1. Field of the Invention
This invention relates to chemistry, involving electrical energy and more particularly, electrolytic cell apparatus with an agitator and a solution controlling system.
2. Description of the Prior Art
U.S. Pat. No. 3,652,442 of Powers et al entitled "Electroplating Cell Including Means to Agitate the Electrolyte in Laminar Flow" shows a bath container including a reciprocating arm with a stirring paddle composed of a base portion triangular in cross-section with sharp edges facing forward and back to minimize turbulence and an apex in the center pointing upwardly which is relatively blunt. A transverse member is spaced above the base portion having an inverted form of the same cross-section so the base member and the transverse member define a slot through which the fluid near the base of the bath container can pass as the paddle is reciprocated back and forth across the base of the container to stir the electrolyte. However, this patent does not provide any means for circulating or replenishing the bath. The patent describes a bath with 109 g/l of NiCl.sub.2.6H.sub.2 O, 3.88 g/l of FeCl.sub.2.4H.sub.2 O, 12.5 g/l H.sub.3 BO.sub.3, 0.4 g/l Na Lauryl Sulfate, and 0.5 g/l saccharin, in a magnetic field of 40 Oe at a bath temperature of 20.degree. C. by means of the continuous plating technique with continuous agitation with the paddle, for plating a flat sheet. With respect to the above formulation, for plating a flat sheet, the nickel-to-iron ratio of ions is believed to be excessive. On the other hand, the plating rate for deposition into photoresist mask defined patterns is not defined at all.
U.S. Pat. No. 3,317,410 of Croll et al for "Agitation System for Electrodeposition of Magnetic Alloys" shows a plating system with continuous circulation of fluid and temperature control, where the solution impinges at right angles onto the cathode, which is uniform for very small areas only.
U.S. Pat. No. 3,649,509 of Morawetz et al for "Electrodeposition Systems" includes means for recycling fluid through a conduit into which heat, acid and specific gravity additives are applied. The system includes no paddle and the fluid is admitted far from the substrate to be plated. Measurement is automatic and continuous, but adjustment is manual and intermittent. However, it states at Col. 2, line 24, "The meters can be by-passed and an electric signal can be applied to a control unit . . . to automatically vary the composition or the temperature of the plating solution." This is a rather vague teaching of an objective or goal rather than an embodiment, since no means for providing automatic control is shown. Furthermore, manual adjustment is unreliable, requires labor and there may be a long response time in comparison to the plating time, and there may be resulting large fluctuations in solution temperature, pH and specific gravity. Also, specific gravity is not a correct measure of the rate of consumption of reagents comprising the alloy being plated and, in particular, of iron which is the most sensitive reagent in terms of maintaining a constant quantity level.
U.S. Pat. No. 3,505,547 of Ambrosia et al teaches a bath for depositing Permalloy alloys in which Fe.sup.++ ions are in a concentration in the range of 10.sup.-3 to 5 .times. 10.sup.-2 mole per liter and Ni ions are in a concentration of 10.sup.-1 to 5 .times. 10.sup.-1 mole per liter, such as 0.2 mole (52 grams) NiSO.sub.4, and 0.2 mole (55 grams) FeSO.sub.4 per liter. In another example, it teaches use of 0.4 mole (105 grams) NiSO.sub.4 and 0.1 mole (27.8 grams) FeSO.sub.4. In still another case, 0.4 mole (105 grams) NiSO.sub.4 and 0.2 mole (55 grams) FeSO.sub.4 are provided. In each case, 10 grams of H.sub.3 BO.sub.3 were used along with metallic ion additives with negative deposition potentials such that they do not codeposit in an amount of 10.sup.-4 to 10.sup.-2 mole per liter. The pH is from 1.3 to 7.
U.S. Pat. No. 3,716,464 of Kovac et al teaches a method of electrodepositing Ni-Fe (80-20) alloys. It also teaches use of a NiSO.sub.4 and FeSO.sub.4 solution with concentration levels such as 20/80 and 5/95 (1/19) of (Fe/Ni) sol. with about 0.3417 g/l of Fe.sup.++ and 6.72 g/l of Ni.sup.++ (based on NiSO.sub.4.6H.sub.2 O = 30 g/l and FeSO.sub.4.7H.sub.2 O = 1.7 g/l, with I peak = 15 ma/cm.sup.2 and with a maximum plating rate of 125 A/min. The pH is 3.0 at 25.degree. C. and 10 g/l of NaK-tartrate is used as a complexing agent.
In a publication by Bartelson et al entitled "Electrodeposition of Ni-Fe Films," a solution of 25-60 g/l of Ni.sup.++ as nickel sulfamate, 1-3 g/l of Fe.sup.++ as ferrous ammonium sulfate, 25 g/l of boric acid, 1 g/l of saccharin, 0.5 g/l of sodium lauryl sulfate, pH 3.7-3.0, temperature 25.degree.-30.degree. C., cathode current density 4.3-8.6 ma/cm.sup.2. However, the sulfamate ion is a complexing agent which complexes both nickel and iron.